Plant Problems

my plants are having some discoloring problems right now!
the bottom leaves are turning like a yellowish color
anybody know why its happening or how to fix it?!

Check out this site it should help you out https://www.rollitup.org/view.php?pg=faq&cmd=article&id=37

that definatly looks like fert burn, have you used pre-fertalized potting soil or fertalized it yet? or them i should say, they are too young to handle any but the most diluted ferts right now, if that indeed is the case i would suggest you flush the soil with a lot of water.

probably getting too cold at night.